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Abstract:

An image sensor includes a plurality of image forming pixels which
receive light beams passing through an imaging pupil area of an imaging
optical system, a plurality of first focus detecting pixels which receive
light beams passing through a first pupil area smaller than the imaging
pupil area, and a plurality of second focus detecting pixels which
receive light beams passing through a second pupil area smaller than the
imaging pupil area. The geometric centre of the first pupil area differs
from the geometric centre of the second pupil area. The eccentricity of
the microlens of the first focus detecting pixel relative to the center
of the pixel differs from the eccentricity of the first focus detecting
pixel relative to the center of the pixel of the microlens of the image
forming pixel adjacent to the first focus detecting pixel.

Claims:

1. An image sensor comprising: a plurality of image forming pixels which
receive light beams passing through an imaging pupil area of an imaging
optical system; a plurality of first focus detecting pixels which receive
light beams passing through a first pupil area smaller than the imaging
pupil area; and a plurality of second focus detecting pixels which
receive light beams passing through a second pupil area smaller than the
imaging pupil area, wherein a geometric centre of the first pupil area
differs from a geometric centre of the second pupil area, and
eccentricity of a lens of said first focus detecting pixel relative to a
center of said pixel differs from eccentricity of a lens of an image
forming pixel adjacent to said first focus detecting pixel relative to a
center of said pixel, said first focus detecting pixel comprising a first
light-shielding layer having a first opening between the lens of said
first focus detecting pixel and a photo-electric conversion portion of
said first focus detecting pixel, said second focus detecting pixel
comprising a second light-shielding layer having a second opening between
the lens of said second focus detecting pixel and a photo-electric
conversion portion of said second focus detecting pixel, and a direction
of eccentricity of each of lenses of said first focus detecting pixel and
said second focus detecting pixel relative to a center of each of said
pixels being opposite to a direction of eccentricity of an average
position of a geometric centre of the first opening and a geometric
centre of the second opening relative to a center of said pixel.

2. The sensor according to claim 1, wherein eccentricity of the lens of
said second focus detecting pixel relative to a center of said pixel
differs from eccentricity of a lens of an image forming pixel adjacent to
said second focus detecting pixel relative to a center of said pixel.

3. The sensor according to claim 1, wherein each of lenses of said focus
detecting pixel and said second focus detecting pixel comprises a
plurality of lenses.

4. An image sensor comprising a plurality of image forming pixels which
receive light beams passing through an imaging pupil area of an imaging
optical system, a plurality of first focus detecting pixels which receive
light beams passing through a first pupil area smaller than the imaging
pupil area, and a plurality of second focus detecting pixels which
receive light beams passing through a second pupil area smaller than the
imaging pupil area, wherein said plurality of image forming pixels are
arrayed in a first direction perpendicular to an optical axis of the
imaging optical system, said plurality of first focus detecting pixels
are arrayed in the first direction so as to shift from said plurality of
image forming pixels in a second direction perpendicular to the first
direction and a direction of the optical axis, said plurality of second
focus detecting pixels are arrayed in the first direction so as to shift
from said plurality of image forming pixels in the second direction, said
first focus detecting pixel comprises a first light-shielding layer
having a first opening between a lens of said first focus detecting pixel
and a photo-electric conversion portion of said first focus detecting
pixel, said second focus detecting pixel comprises a second
light-shielding layer having a second opening located at a position
different from a position of the first opening in the first direction
between a lens of said second focus detecting pixel and a photo-electric
conversion portion of said second focus detecting pixel, an average
position of a geometric centre of the first opening and a geometric
centre of the second opening is eccentric with respect to a geometric
centre of a photo-electric conversion portion of said first focus
detecting pixel in the first direction, eccentricity of a lens of said
first focus detecting pixel relative to a center of said pixel differs
from eccentricity of a lens of said image forming pixel relative to a
center of said pixel in the first direction at the same image height in
the first direction, eccentricity of a lens of said second focus
detecting pixel relative to a center of said pixel differs from
eccentricity of a lens of said image forming pixel relative to a center
of said pixel in the first direction at the same image height in the
first direction, and a direction of eccentricity of each of lenses of
said first focus detecting pixel and said second focus detecting pixel
relative to a center of said pixel in the first direction is opposite to
a direction of eccentricity of an average position of a geometric centre
of the first opening and a geometric centre of the second opening
relative to a center of said pixel.

5. The sensor according to claim 4, wherein a direction of eccentricity
of each of lenses of said first focus detecting pixel and said second
focus detecting pixel relative to a center of said pixel is a direction
to approach an optical axis of said imaging optical system, and a
direction of eccentricity of an average position of a geometric centre of
the first opening and a geometric centre of the second opening relative
to a center of said pixel is a direction to separate from the optical
axis of said imaging optical system.

Description:

[0002] The present invention relates to an image sensor and an image
capturing apparatus using the same.

[0003] 2. Description of the Related Art

[0004] There has been proposed an image capturing apparatus using, as a
method of detecting the focus state of an imaging lens, a pupil division
phase-difference method (imaging plane phase-difference method) using a
two-dimensional image sensor having a microlens formed on each pixel.

[0005] In an optical system, such as a camera lens unit, the entrance
pupil is the optical image of the aperture stop viewed from the front of
the lens. The corresponding image of the aperture viewed from the rear of
the lens is known as the exit pupil. The image of the aperture stop will
be in focus at a particular distance beyond the camera lens unit and this
distance is known as the pupil distance of the imaging lens. Modern image
sensors often include microlens arrays around the pixels in order to
improve light capture efficiency. As a consequence of this, the image
sensor is only able to accept light from a limited range of angles and
each photodiode, and hence the image sensor, has an entrance pupil that
is an image of the openings to the photodiodes viewed through the
microlenses. The entrance pupil distance of the image sensor is a
distance at which those openings are in focus through the microlenses.

[0006] U.S. Pat. No. 4,410,804 discloses an image capturing apparatus
using a two-dimensional image sensor having one microlens and a plurality
of divided photo-electric conversion portions formed for one pixel.
Divided photo-electric conversion portions are configured to receive
light from different areas of the exit pupil of the imaging lens through
one microlens, thereby performing pupil division. This apparatus performs
focus detection by obtaining an image shift amount from the respective
signals received by these divided photo-electric conversion portions, and
acquires an imaging signal by adding the signals received by the divided
photo-electric conversion portions. This patent literature also discloses
that the apparatus can obtain a stereoscopic image by separately
displaying the parallax signals, received by the laterally divided
photo-electric conversion portions on each pixel, for the right and left
eyes. Japanese Patent Laid-Open No. 2000-156823 discloses an image
capturing apparatus having a pair of focus detecting pixels partially
arranged in a two-dimensional image sensor constituted by a plurality of
image forming pixels. The pair of focus detecting pixels are configured
to receive light from different areas of the exit pupil of the imaging
lens through a light-shielding layer having an opening, thereby
performing pupil division. This apparatus acquires imaging signals using
image forming pixels arranged on the most part of the two-dimensional
sensor and performs focus detection by obtaining an image shift amount
from signals from the focus detecting pixels partially arranged on the
sensor.

[0007] Consider, for example, a camera with interchangeable lenses. In
this case, if the exit pupil distance of the imaging lens differs from
the incident pupil distance of the image sensor, an increase in the image
height at the image sensor will cause a pupil shift between the exit
pupil of the imaging lens and the incident pupil of the image sensor. In
addition, the positional shift between a microlens and divided
photo-electric conversion portions or between a microlens and a
light-shielding layer having an opening due to mass-production variations
causes a pupil shift between the exit pupil of the imaging lens and the
incident pupil of the image sensor. In focus detection using the imaging
plane phase-difference method, as a pupil shift occurs, the asymmetry of
the respective partial pupil areas having undergone pupil division
increases, resulting in a deterioration in focus detection accuracy.

[0008] Japanese Patent Laid-Open No. 2009-15164 discloses a technique of
coping with a pupil shift by arranging a plurality of focus detecting
pixels shifted from each other by different shift amounts for positioning
between microlenses and divided photo-electric conversion portions. This
technique performs focus detection using the imaging plane
phase-difference method by selecting focus detecting pixels which
minimize the asymmetry of the respective partial pupil areas having
undergone pupil division in accordance with the imaging lens and the
image height for focus detection.

[0009] In an actual image sensor, however, since each pixel has a finite
size, there is an upper limit on the shift amount by which divided
photo-electric conversion portions or light-shielding layers having
openings are shifted inside pixels. This makes it impossible to cope with
a pupil shift at the peripheral image height of the image sensor,
resulting in a deterioration in focus detection accuracy. This then
limits the image height range in which the pupil division
phase-difference method can perform focus detection.

SUMMARY OF THE INVENTION

[0010] The present invention has been made in consideration of the above
problem, and enlarges the image height range in which focus detection can
be performed in focus detection on an imaging plane by using the pupil
division phase-difference method.

[0011] According to the first aspect of the present invention, there is
provided an image sensor comprising: a plurality of image forming pixels
which receive light beams passing through an imaging pupil area of an
imaging optical system; a plurality of first focus detecting pixels which
receive light beams passing through a first pupil area smaller than the
imaging pupil area; and a plurality of second focus detecting pixels
which receive light beams passing through a second pupil area smaller
than the imaging pupil area, wherein a geometric centre of the first
pupil area differs from a geometric centre of the second pupil area, and
eccentricity of a lens of the first focus detecting pixel relative to a
center of the pixel differs from eccentricity of a lens of an image
forming pixel adjacent to the first focus detecting pixel relative to a
center of the pixel, the first focus detecting pixel comprising a first
light-shielding layer having a first opening between the lens of the
first focus detecting pixel and a photo-electric conversion portion of
the first focus detecting pixel, the second focus detecting pixel
comprising a second light-shielding layer having a second opening between
the lens of the second focus detecting pixel and a photo-electric
conversion portion of the second focus detecting pixel, and a direction
of eccentricity of each of lenses of the first focus detecting pixel and
the second focus detecting pixel relative to a center of each of the
pixels being opposite to a direction of eccentricity of an average
position of a geometric centre of the first opening and a geometric
centre of the second opening relative to a center of the pixel.

[0012] According to the second aspect of the present invention, there is
provided an image sensor comprising a plurality of image forming pixels
which receive light beams passing through an imaging pupil area of an
imaging optical system, a plurality of first focus detecting pixels which
receive light beams passing through a first pupil area smaller than the
imaging pupil area, and a plurality of second focus detecting pixels
which receive light beams passing through a second pupil area smaller
than the imaging pupil area, wherein the plurality of image forming
pixels are arrayed in a first direction perpendicular to an optical axis
of the imaging optical system, the plurality of first focus detecting
pixels are arrayed in the first direction so as to shift from the
plurality of image forming pixels in a second direction perpendicular to
the first direction and a direction of the optical axis, the plurality of
second focus detecting pixels are arrayed in the first direction so as to
shift from the plurality of image forming pixels in the second direction,
the first focus detecting pixel comprises a first light-shielding layer
having a first opening between a lens of the first focus detecting pixel
and a photo-electric conversion portion of the first focus detecting
pixel, the second focus detecting pixel comprises a second
light-shielding layer having a second opening located at a position
different from a position of the first opening in the first direction
between a lens of the second focus detecting pixel and a photo-electric
conversion portion of the second focus detecting pixel, an average
position of a geometric centre of the first opening and a geometric
centre of the second opening is eccentric with respect to a geometric
centre of a photo-electric conversion portion of the first focus
detecting pixel in the first direction, eccentricity of a lens of the
first focus detecting pixel relative to a center of the pixel differs
from eccentricity of a lens of the image forming pixel relative to a
center of the pixel in the first direction at the same image height in
the first direction, eccentricity of a lens of the second focus detecting
pixel relative to a center of the pixel differs from eccentricity of a
lens of the image forming pixel relative to a center of the pixel in the
first direction at the same image height in the first direction, and a
direction of eccentricity of each of lenses of the first focus detecting
pixel and the second focus detecting pixel relative to a center of the
pixel in the first direction is opposite to a direction of eccentricity
of an average position of a geometric centre of the first opening and a
geometric centre of the second opening relative to a center of the pixel.

[0013] According to the third aspect of the present invention, there is
provided an image capturing apparatus as specified above.

[0014] Further features of the present invention will become apparent from
the following description of exemplary embodiments with reference to the
attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a block diagram showing the schematic arrangement of an
image capturing apparatus according to an embodiment of the present
invention;

[0016] FIG. 2 is a schematic view of a pixel array in the embodiment of
the present invention;

[0017] FIGS. 3A and 3B are respectively a schematic plan view and a
schematic sectional view showing the first focus detecting pixel in
arrangement 1 in the first embodiment;

[0018] FIGS. 4A and 4B are respectively a schematic plan view and a
schematic sectional view showing the second focus detecting pixel in
arrangement 1 in the first embodiment;

[0019] FIGS. 5A and 5B are respectively a schematic plan view and a
schematic sectional view showing an image forming pixel in the first
embodiment;

[0020] FIGS. 6A to 6C are schematic views for explaining pupil division in
arrangement 1 in the first embodiment;

[0021] FIGS. 7A and 7B are respectively a schematic plan view and a
schematic sectional view showing the first focus detecting pixel in
arrangement 2 in the first embodiment;

[0022] FIGS. 8A and 8B are respectively a schematic plan view and a
schematic sectional view showing the second focus detecting pixel in
arrangement 2 in the first embodiment;

[0023] FIGS. 9A to 9C are schematic views for explaining pupil division in
arrangement 2 in the first embodiment;

[0024] FIGS. 10A and 10B are respectively a schematic plan view and a
schematic sectional view showing the first focus detecting pixel in
arrangement 3 in the first embodiment;

[0025] FIGS. 11A and 11B are respectively a schematic plan view and a
schematic sectional view showing the second focus detecting pixel in
arrangement 3 in the first embodiment;

[0026] FIGS. 12A to 12C are schematic views for explaining pupil division
in arrangement 3 in the first embodiment;

[0027] FIGS. 13A to 13C are schematic views for explaining a pupil shift;

[0028] FIGS. 14A and 14B are schematic views for explaining a pupil shift;

[0029] FIGS. 15A and 15B are respectively a schematic plan view and a
schematic sectional view showing the first focus detecting pixel in
arrangement 1 in the second embodiment;

[0030] FIGS. 16A and 16B are respectively a schematic plan view and a
schematic sectional view showing the second focus detecting pixel in
arrangement 1 in the second embodiment;

[0031] FIGS. 17A and 17B are respectively a schematic plan view and a
schematic sectional view showing image forming pixel in the second
embodiment;

[0032] FIGS. 18A and 18B are respectively a schematic plan view and a
schematic sectional view showing the first focus detecting pixel in
arrangement 2 in the second embodiment; and

[0033] FIGS. 19A and 19B are respectively a schematic plan view and a
schematic sectional view showing the second focus detecting pixel in
arrangement 2 in the second embodiment.

DESCRIPTION OF THE EMBODIMENTS

[0034] The embodiments of the present invention will be described in
detail below with reference to the accompanying drawings.

First Embodiment

Overall Arrangement

[0035] FIG. 1 is a block diagram showing the arrangement of an image
capturing apparatus as a camera which includes an image sensor according
to the first embodiment of the present invention. Referring to FIG. 1,
reference numeral 101 denotes a first lens group which is disposed at the
distal end of an imaging optical system and is held so as to be movable
forward and backward in the optical axis direction; 102, a stop/shutter
which performs light amount adjustment at the time of imaging by
adjusting the opening diameter and also functions as an exposure time
adjustment shutter at the time of still image capturing; and 103, a
second lens group. The stop/shutter 102 and the second lens group 103
integrally move forward and backward in the optical axis direction to
implement a variable power effect (zoom function) interlockingly with the
forward/backward movement of the first lens group 101.

[0036] Reference numeral 105 denotes a third lens group which moves
backward and forward in the optical axis direction to perform focus
adjustment; 106, an optical low-pass filter which is an optical element
for reducing the false color or moire of a captured image; and 107, an
image sensor constituted by a two-dimensional CMOS photosensor and
peripheral circuits.

[0037] Reference numeral 111 denotes a zoom actuator which makes a cam
cylinder (not shown) pivot to drive the first lens group 101, the second
lens group 103, and the third lens group 105 forward and backward in the
optical axis direction so as to perform variable power operation.
Reference numeral 112 denotes a stop shutter actuator which adjusts an
imaging light amount by controlling the opening diameter of the
stop/shutter 102 and controls an exposure time at the time of still image
capturing. Reference numeral 114 denotes a focus actuator which performs
focus adjustment by driving the third lens group 105 forward and backward
in the optical axis direction.

[0038] Reference numeral 115 denotes an electronic flash for illuminating
an object at the time of imaging. As this flash, a flash illumination
device using a xenon tube is suitably used. However, an illumination
device including an LED which continuously emits light may be used.
Reference numeral 116 denotes an AF auxiliary light device which projects
an image of a mask having a predetermined opening pattern on a field
through a projection lens and improves the focus detection performance
for a dark object or a low-contrast object.

[0039] Reference numeral 121 denotes a CPU in the camera which performs
various types of control on the camera main body and includes a computing
unit, ROM, RAM, A/D converter, D/A converter, and communication interface
circuit. The CPU 121 drives various types of circuits of the camera based
on predetermined programs stored in the ROM to execute a series of
operations including AF, imaging, image processing, and recording.

[0040] Reference numeral 122 denotes an electronic flash control circuit
which ON/OFF-controls the electronic flash 115 in synchronism with
imaging operation; 123, an auxiliary light driving circuit which
ON/OFF-controls the AF auxiliary light device 116 in synchronism with
focus detecting operation; 124, an image sensor driving circuit which
controls the imaging operation of the image sensor 107 and transmits the
acquired image signal to the CPU 121 upon A/D-converting the signal; and
125, an image processing circuit which performs processing such as
γ conversion, color interpolation, and JPEG compression for the
image acquired by the image sensor 107.

[0041] Reference numeral 126 denotes a focus driving circuit which
drives/controls the focus actuator 114 based on a focus detection result
to perform focus adjustment by driving the third lens group 105 forward
and backward in the optical axis direction; 128, a stop shutter driving
circuit which drives/controls the stop shutter actuator 112 to control
the opening of the stop/shutter 102; and 129, a zoom driving circuit 129
which drives the zoom actuator 111 in accordance with the zooming
operation performed by the operator.

[0042] Reference numeral 131 denotes a display device such as an LCD which
displays information concerning the imaging modes of the camera, a
preview image before imaging, a check image after imaging, an in-focus
state display image at the time of focus detection, and the like; 132, an
operation switch group constituted by a power switch, release (imaging
trigger) switch, zoom operation switch, imaging mode selection switch,
and the like; and 133, a detachable flash memory which records a captured
image.

[0043] [Image Sensor]

[0044] FIG. 2 is a schematic view showing the pixel array of the image
sensor in the first embodiment. FIG. 2 shows the pixel array of a
two-dimensional CMOS sensor (image sensor) in the first embodiment within
the range of 20 (columns)×20 (rows) pixels. Many arrays of 20
(columns)×20 (rows) pixels shown in FIG. 2 are arranged on a
surface to allow acquisition of a high-resolution image. This embodiment
will exemplify an image sensor with a pixel pitch of 4 μm, an
effective pixel count of horizontal 5575 columns×vertical 3725
rows=about 20000000 pixels, and an imaging screen size of 22.3 mm
(horizontal)×14.9 mm (vertical).

[0045] In this embodiment, a 2 (rows)×2 (columns) focus detecting
pixel group 200 shown in FIG. 2 includes a pixel 200R having R (Red)
spectral sensitivity and located on the upper left, pixels 200G having G
(Green) spectral sensitivity and located on the upper right and the lower
left, and a pixel 200B having B (Blue) spectral sensitivity and located
on the lower right. A 2 (rows)×2 (columns) pixel group 210 (220,
230, 240, or 250) shown in FIG. 2 includes two image forming pixels 210G
(220G, 230G, 240G, or 250G) having G spectral sensitivity and located on
the upper right and the lower left. This pixel group also includes a
first focus detecting pixel 210SA (220SA, 230SA, 240SA, or 250SA) having
W (White) spectral sensitivity and located on the upper left and a second
focus detecting pixel 210SB (220SB, 230SB, 240SB, or 250SB) having W
spectral sensitivity and located on the lower right.

[0046] [Arrangement 1]

[0047] The focus detecting pixel group 230 in arrangement 1 will be
described below. FIG. 3A is a plan view of the first focus detecting
pixel 230SA as one pixel of the image sensor shown in FIG. 2 when viewed
from the light-receiving surface side (+z side) of the image sensor. FIG.
3B is a sectional view taken along a-a in FIG. 3A when viewed from the -y
side. FIG. 4A is a plan view of the second focus detecting pixel 230SB as
one pixel of the image sensor shown in FIG. 2 when viewed from the
light-receiving surface side (+z side) of the image sensor. FIG. 4B is a
sectional view taken along b-b in FIG. 4A when viewed from the -y side.
FIG. 5A is a plan view of the first image forming pixel 230G as one pixel
of the image sensor shown in FIG. 2 when viewed from the light-receiving
surface side (+z side) of the image sensor. FIG. 5B is a sectional view
taken along c-c in FIG. 5A when viewed from the -y side.

[0048] As shown in FIGS. 3A to 5B, in each of the first focus detecting
pixel 230SA, the second focus detecting pixel 230SB, and the image
forming pixel 230G in this embodiment, a photodiode (photo-electric
conversion portion) PD having a pin structure is formed, in which a
p-type layer 300 and an n-type layer 301 sandwich an n-intrinsic layer
302. The region of the photo-electric conversion portion PD is equivalent
to the region of a depletion layer formed in the n-intrinsic layer 302
and its surrounding region extending by the distance that minority
carriers diffuse, and almost overlaps the total region of the n-intrinsic
layer 302 and n-type layer 301. The n-intrinsic layer 302 may be omitted
to form a p-n junction photodiode, as needed. A microlens 305 for
focusing incident light is formed on the light-receiving side of each
pixel.

[0049] In the first focus detecting pixel 230SA shown in FIGS. 3A and 3B,
a first light-shielding layer 330a having a first opening is formed
between the microlens 305 and the photo-electric conversion portion PD,
with the geometric centre of the first opening being eccentric with
respect to the geometric centre of the photo-electric conversion portion
in the -x direction.

[0050] In the second focus detecting pixel 230SB shown in FIGS. 4A and 4B,
a second light-shielding layer 330b having the second opening is formed
between the microlens 305 and the photo-electric conversion portion PD,
with the geometric centre of the second opening being eccentric with
respect to the geometric centre of the light-receiving surface of the
photo-electric conversion portion in the +x direction.

[0051] In arrangement 1, the geometric centre of the first opening of the
first light-shielding layer 330a differs from the geometric centre of the
second opening of the second light-shielding layer 330b. In addition, the
average position of the geometric centre of the first opening of the
first light-shielding layer 330a and the geometric centre of the second
opening of the second light-shielding layer 330b is made to almost
coincide with the geometric centre of the light-receiving surface of the
photo-electric conversion portion.

[0052] This embodiment forms the first light-shielding layer having the
first opening and the second light-shielding layer having the second
opening by using wiring layers for driving the image sensor. That is, the
formed layers serve as both the wiring layers and the light-shielding
layers.

[0053] In this embodiment, the first focus detecting pixel has the first
light-shielding layer having the first opening between the microlens of
the first focus detecting pixel and the photo-electric conversion portion
of the first focus detecting pixel. In addition, the second focus
detecting element includes the second light-shielding layer having the
second opening between the microlens of the second focus detecting pixel
and the photo-electric conversion portion of the second focus detecting
pixel.

[0054] The microlens 305 focuses light entering the first focus detecting
pixel 230SA (second focus detecting pixel 230SB) shown in FIGS. 3A and 3B
(FIGS. 4A and 4B). Part of the focused light passes through the first
opening (second opening) of the first light-shielding layer 330a (second
light-shielding layer 330b) and is received by the photo-electric
conversion portion PD. The photo-electric conversion portion PD generates
electron-hole pairs in accordance with the amount of light received, and
dissociates them through a depletion layer. The photo-electric conversion
portion PD then accumulates the negatively charged electrons in the
n-type layer 301 while discharging the holes outside the image sensor
through the p-type layer 300 connected to a constant voltage source (not
shown).

[0055] In contrast to a focus detecting pixel, in the image forming pixel
230G shown in FIGS. 5A and 5B, a wiring layer 330c is formed on only a
peripheral portion of the pixel, and no light-shielding layer is formed
in the middle portion of the pixel. A G (Green) color filter (not shown)
is formed between the microlens 305 and the photo-electric conversion
portion PD.

[0056] FIGS. 6A to 6C are schematic views showing the correspondence
relationship between pupil division and the opening of the
light-shielding layer formed on a pixel with arrangement 1. FIG. 6A is a
sectional view of the first focus detecting pixel 230SA taken along a-a
in FIG. 3A when viewed from the +y side and shows the exit pupil plane of
the imaging optical system. FIG. 6B is a sectional view of the second
focus detecting pixel 230SB taken along b-b in FIG. 4A when viewed from
the +y side and shows the exit pupil plane of the imaging optical system.
FIG. 6c is a sectional view of the image forming pixel 230G taken along
c-c in FIG. 5A when viewed from the +y side and shows the exit pupil
plane of the imaging optical system. To match with the coordinate axes of
the exit pupil plane in each of FIGS. 6A to 6C, the x- and y-axes of the
sectional view are inverted with respect to each of FIGS. 3A to 5B.

[0057] Referring to FIGS. 6A to 6C, reference numeral 400 denotes the exit
pupil of the imaging optical system; 500, the pupil intensity
distribution (imaging pupil area) of the image forming pixel 230G; 530a,
the pupil intensity distribution (first pupil area) of the first focus
detecting pixel 230SA; and 530b, the pupil intensity distribution (second
pupil area) of the second focus detecting pixel 230SB. Note that
reference symbol PD denotes a photo-electric conversion portion. A light
beam from an object passes through the exit pupil 400 of the imaging
optical system and enters each pixel.

[0058] Referring to FIG. 6c, the imaging pupil area 500 of the image
forming pixel is almost conjugate to the light-receiving surface of the
photo-electric conversion portion PD through the microlens, and
represents a pupil area which can receive light through the image forming
pixels. The pupil distance is several 10 mm, whereas the diameter of the
microlens is several μm. The aperture value of the microlens is
therefore several ten thousands, and hence diffraction blurring occurs at
several 10 mm level. For this reason, an image on the light-receiving
surface of the photo-electric conversion portion PD is not a clear area
but represents a light reception ratio distribution.

[0059] The imaging pupil area 500 of the image forming pixel is maximized
to receive a large amount of light beam passing through the exit pupil
400 of the imaging optical system. In addition, the geometric centre of
the imaging pupil area 500 almost coincides with the optical axis of the
imaging optical system at a predetermined pupil distance.

[0060] Referring to FIG. 6A, in the first pupil area 530a of the first
focus detecting pixel 230SA, the geometric centre of the first
light-shielding layer 330a is almost conjugate to the first opening
eccentric in the -x direction through the microlens. FIG. 6A also shows a
pupil area which can receive light through the first focus detecting
pixel 230SA. The first pupil area 530a of the first focus detecting pixel
230SA is smaller than the imaging pupil area 500 of the image forming
pixel and has a geometric centre eccentric to the +X side on the pupil
plane.

[0061] Referring to FIG. 6B, in the second pupil area 530b of the second
focus detecting pixel 230SB, the geometric centre of the second
light-shielding layer 330b is almost conjugate to the second opening
eccentric in the +x direction through the microlens. FIG. 6B also shows a
pupil area which can receive light through the second focus detecting
pixel 230SB. The second pupil area 530b of the second focus detecting
pixel 230SB is smaller than the imaging pupil area 500 of the image
forming pixel and has a geometric centre eccentric to the -X side on the
pupil plane.

[0062] The geometric centre of the first pupil area 530a of the first
focus detecting pixel 230SA and the geometric centre of the second pupil
area 530b of the second focus detecting pixel 230SB differ from each
other and are eccentric in the opposite directions. This makes it
possible to perform pupil division for the exit pupil 400 of the imaging
optical system in the X direction. Likewise, making the geometric centre
of the first opening of the first light-shielding layer eccentric in the
-y direction and the geometric centre of the second opening of the second
light-shielding layer eccentric in the +y direction can perform pupil
division for the exit pupil 400 of the imaging optical system in the Y
direction.

[0063] In arrangement 1, the geometric centre of the first pupil area 530a
differs from the geometric centre of the second pupil area 530b. In
addition, the average of the geometric centre of the first pupil area
530a and the geometric centre of the second pupil area 530b almost
coincides with the geometric centre of the imaging pupil area 500 at a
predetermined pupil distance.

[0064] The image sensor of this embodiment includes a plurality of image
forming pixels which receive light beams passing through the imaging
pupil area of the imaging optical system, a plurality of first focus
detecting pixels which receive light beams passing through the first
pupil area smaller than the imaging pupil area, and a plurality of second
focus detecting pixels which receive light beams passing through the
second pupil area smaller than the imaging pupil area, and is configured
such that the geometric centre of the first pupil area differs from the
geometric centre of the second pupil area.

[0065] [Arrangement 2]

[0066] The focus detecting pixel group 220 in arrangement 2 will be
described below. FIG. 7A is a plan view of the first focus detecting
pixel 220SA as one pixel of the image sensor shown in FIG. 2 when viewed
from the light-receiving surface side (+z side) of the image sensor. FIG.
7B is a sectional view taken along a-a in FIG. 7A when viewed from the -y
side. FIG. 8A is a plan view of the second focus detecting pixel 220SB as
one pixel of the image sensor shown in FIG. 2 when viewed from the
light-receiving surface side (+z side) of the image sensor. FIG. 8B is a
sectional view taken along b-b in FIG. 8A when viewed from the -y side.
The image forming pixel 220G is the same as the first image forming pixel
230G in arrangement 1.

[0067] In arrangement 2, the geometric centre of the first opening of a
first light-shielding layer 320a of the first focus detecting pixel 220SA
differs from the geometric centre of the second opening of a second
light-shielding layer 320b of the second focus detecting pixel 220SB. In
addition, the average position of the geometric centre of the first
opening of the first light-shielding layer 320a and the geometric centre
of the second opening of the second light-shielding layer 320b is
eccentric with respect to the geometric centre of the light-receiving
surface of the photo-electric conversion portion in the -x direction.

[0068] In contrast to this, the first focus detecting pixel 240SA and
second focus detecting pixel 240SB of the focus detecting pixel group 240
shown in FIG. 2 are configured such that the average position of the
geometric centre of the first opening of the first light-shielding layer
and the geometric centre of the second opening of the second
light-shielding layer is eccentric with respect to the geometric centre
of the light-receiving surface of the photo-electric conversion portion
in the +x direction.

[0069] FIGS. 9A to 9C are schematic views for explaining the
correspondence relationship between pupil division and the opening of the
light-shielding layer formed on a pixel in arrangement 2. FIG. 9A is a
sectional view of the first focus detecting pixel 220SA taken along a-a
in FIG. 7A when viewed from the +y side. FIG. 9B is a sectional view of
the second focus detecting pixel 220SB taken along b-b in FIG. 8A when
viewed from the +y side, and shows the exit pupil plane of the imaging
optical system. To match with the coordinate axes of the exit pupil plane
in each of FIGS. 9A to 9C, the x- and y-axes of the sectional view are
inverted with respect to each of FIGS. 7A to 8B.

[0070] In arrangement 2, the geometric centre of a first pupil area 520a
of the first focus detecting pixel 220SA differs from a second pupil area
520b of the second focus detecting pixel 220SB. The average of the
geometric centre of the first pupil area 520a and the geometric centre of
the second pupil area 520b is eccentric to the +X side with respect to
the geometric centre of the imaging pupil area 500 at a predetermined
pupil distance.

[0071] In contrast to this, the first focus detecting pixel 240SA and
second focus detecting pixel 240SB of the focus detecting pixel group 240
shown in FIG. 2 are configured such that the average of the geometric
centre of the first pupil area and the geometric centre of the second
pupil area is eccentric to the -X side with respect to the geometric
centre of the imaging pupil area 500 at a predetermined pupil distance.

[0072] [Arrangement 3]

[0073] The focus detecting pixel group 210 in arrangement 3 will be
described below. FIG. 10A is a plan view showing the first focus
detecting element 210SA as one pixel of the image sensor shown in FIG. 2
when viewed from the light-receiving surface side (+z side) of the image
sensor. FIG. 10B is a sectional view taken along a-a in FIG. 10A when
viewed from the -y side. FIG. 11A is a plan view showing the second focus
detecting element 210SB as one pixel of the image sensor shown in FIG. 2
when viewed from the light-receiving surface side (+z side) of the image
sensor. FIG. 11B is a sectional view of the second focus detecting
element 210SB taken along b-b in FIG. 11A when viewed from the -y side.
The image forming pixel 210G is the same as the first image forming pixel
230G in arrangement 1.

[0074] In arrangement 3, the geometric centre of the first opening of a
first light-shielding layer 310a of the first focus detecting element
210SA differs from the geometric centre of the second opening of a second
light-shielding layer 310b of the second focus detecting element 210SB.
The average position of the geometric centre of the first opening of the
first light-shielding layer 310a and the geometric centre of the second
opening of the second light-shielding layer 310b is eccentric with
respect to the geometric centre of the photo-electric conversion portion
in the -x direction. The microlenses of the first focus detecting element
210SA and second focus detecting element 210SB are eccentric with respect
to the geometric centre of the light-receiving surface of the
photo-electric conversion portion in the +x direction.

[0075] In contrast to this, the first focus detecting element 250SA and
second focus detecting element 250SB of the focus detecting element group
250 shown in FIG. 2 are configured such that the average position of the
geometric centre of the first opening of the first light-shielding layer
and the geometric centre of the second opening of the second
light-shielding layer is eccentric with respect to the geometric centre
of the light-receiving surface of the photo-electric conversion portion
in the +x direction. The microlenses of the first focus detecting element
250SA and second focus detecting element 250SB are eccentric with respect
to the geometric centre of the light-receiving surface of the
photo-electric conversion portion in the -x direction.

[0076] The microlenses of the first focus detecting element and second
focus detecting element are eccentric in a direction opposite to the
direction in which the average position of the geometric centre of the
first opening and the geometric centre of the second opening is
eccentric.

[0077] Since the first light-shielding layer 310a of the first focus
detecting element 210SA in this embodiment is formed from a wiring layer
for driving the image sensor, the first opening of the first
light-shielding layer 310a cannot be made further eccentric in the -x
direction. Instead of this, the microlens of the first focus detecting
element 210SA is made eccentric in the +x direction as the opposite
direction. It is possible to further increase the eccentricity amount of
the first opening of the first light-shielding layer 310a with respect to
the microlens of the first focus detecting element 210SA as compared with
that in arrangement 2. The microlens of the image forming pixel 210G is
the same as that in arrangement 1.

[0078] The first focus detecting element 210SA and the image forming pixel
210G constituting the pixel group 210 are adjacent to each other, as
shown in FIG. 2. The eccentricity of the microlens of the first focus
detecting element 210SA shown in FIGS. 10A and 10B differs from the
eccentricity of the microlens of the image forming pixel 210G shown in
FIG. 5. Likewise, the second focus detecting element 210SB and the image
forming pixel 210G constituting the pixel group 210 are adjacent to each
other, as shown in FIG. 2. The eccentricity of the microlens of the
second focus detecting element 210SB shown in FIGS. 11A and 11B differs
from the eccentricity of the microlens of the image forming pixel 210G
shown in FIGS. 5A and 5B.

[0079] In this embodiment, therefore, the eccentricity of the microlens of
the first focus detecting element 210SA differs from the eccentricity of
the microlens of the adjacent image forming pixel 210G in this
embodiment. In addition, the eccentricity of the microlens of the second
focus detecting element 210SB differs from the eccentricity of the
microlens of the adjacent image forming pixel 210G.

[0080] FIGS. 12A to 12C are schematic views showing the correspondence
relationship between pupil division and the opening of the
light-shielding layer formed on the pixel in arrangement 3. FIG. 12A is a
sectional view of the first focus detecting element 210SA taken along a-a
in FIG. 10A when viewed from the +y side, and shows the exit pupil plane
of the imaging optical system. FIG. 12B is a sectional view of the second
focus detecting element 210SB taken along b-b in FIG. 11A when viewed
from the +y side, and shows the exit pupil plane of the imaging optical
system. To match with the coordinate axes of the exit pupil plane in each
of FIGS. 12A to 12C, the x- and y-axes of the sectional view are inverted
with respect to each of FIGS. 10A to 11B.

[0081] In arrangement 3, the geometric centre of a first pupil area 510a
of the first focus detecting element 210SA differs from the geometric
centre of a second pupil area 510b of the second focus detecting element
210SB. The average of the geometric centre of the first pupil area 510a
and the geometric centre of the second pupil area 510b is eccentric to
the +X side with respect to the geometric centre of the imaging pupil
area 500 at a predetermined pupil distance.

[0082] In contrast to this, the first focus detecting element 250SA and
second focus detecting element 250SB of the focus detecting element group
250 shown in FIG. 2 are configured such that the average of the geometric
centre of the first pupil area and the geometric centre of the second
pupil area is eccentric to the -X side with respect to the geometric
centre of the imaging pupil area 500 at a predetermined pupil distance.

[0083] [Focus Detection]

[0084] The first focus detecting elements 210SA (220SA, 230SA, 240SA, or
250SA) shown in FIG. 2 are regularly arrayed in the x direction, and the
object image acquired from the plurality of first focus detecting pixels
will be referred to as an image A. Likewise, the second focus detecting
elements 210SB (220SB, 230SB, 240SB, or 250SB) shown in FIG. 2 are
regularly arrayed in the x direction, and the object image acquired from
the plurality of second focus detecting pixels will be referred to as an
image B. It is possible to perform focus detection by calculating a
defocus amount (blurring amount) from the image shift amount (relative
position) between the images A and B.

[0085] [Handling of Pupil Shift]

[0086] Handling of a pupil shift at the peripheral image height of the
image sensor in this embodiment will be described below. FIGS. 13A to
13C, 14A, and 14B show the relationship between the first pupil area of
the first focus detecting pixel, the second pupil area of the second
focus detecting pixel, and the exit pupil of the imaging optical system
at the peripheral image height of the image sensor.

[0087]FIG. 13A shows a case in which an exit pupil distance Dl of the
imaging optical system almost coincides with a set pupil distance Ds of
the image sensor. In this case, the exit pupil 400 of the imaging optical
system is almost uniformly pupil-divided by the first pupil area 530a of
the first focus detecting pixel 230SA and the second pupil area 530b of
the second focus detecting pixel 230SB.

[0088] In contrast to this, the exit pupil 400 of the imaging optical
system is non-uniformly pupil-divided at the peripheral height of the
image sensor in the case shown in FIG. 13B in which the exit pupil
distance Dl of the imaging optical system is shorter than the set pupil
distance Ds of the image sensor or the case shown in FIG. 13c in which
the exit pupil distance Dl of the imaging optical system is longer than
the set pupil distance Ds of the image sensor.

[0089] As pupil division becomes non-uniform, the intensities of the
images A and B (FIG. 13) become non-uniform. As a consequence, the
intensity of one of the images A and B becomes larger, and the intensity
of the other image becomes smaller. As the intensities of the images A
and B become greatly non-uniform due to the peripheral image height and
the like, one of the signals of the images A and B obtained cannot have a
sufficient intensity, resulting in a deterioration in focus detection
performance.

[0090] In this embodiment, the first focus detecting element 210SA and the
second focus detecting element 210SB in arrangement 3 are arranged in
advance, in which the average of the geometric centre of the first pupil
area 510a and the geometric centre of the second pupil area 510b is
greatly eccentric to the +X side with respect to the geometric centre of
the imaging pupil area 500 at a predetermined pupil distance.

[0091] FIGS. 14A and 14B show a case in which the exit pupil distance Dl
of the imaging optical system differs from the set pupil distance Ds of
the image sensor, and the exit pupil 400 of the imaging optical system
becomes greatly eccentric to the +X side on a pupil plane at the position
corresponding to the set pupil distance Ds of the image sensor at the
peripheral image height. FIG. 14A shows a case in which the exit pupil
400 of the imaging optical system which is greatly eccentric to the +X
side is pupil-divided by the first pupil area 530a of the first focus
detecting pixel 230SA and the second pupil area 530b of the second focus
detecting pixel 230SB in arrangement 1. In this case, a pupil shift is
large and non-uniform pupil division occurs. In contrast to this, FIG.
14B shows a case in which the exit pupil 400 of the imaging optical
system which is eccentric to the +X side is pupil-divided by the first
pupil area 510a of the first focus detecting element 210SA and the second
pupil area 510b of the second focus detecting element 210SB in
arrangement 3. In this case, even at the peripheral image height, a pupil
shift can be reduced, and uniform pupil division can be performed. This
can improve the focus detection performance.

[0092] The above arrangement can enlarge the image height range in which
focus detection can be performed by the pupil division phase-difference
method in accordance with a pupil shift at the peripheral height of the
image sensor.

Second Embodiment

[0093] The second embodiment of the present invention will be described
below.

[0094] [Arrangement 1]

[0095] A focus detecting pixel group 230 in arrangement 1 will be
described below. FIG. 15A is a plan view of a first focus detecting pixel
230SA as one pixel of the image sensor shown in FIG. 2 when viewed from
the light-receiving surface side (+z side) of the image sensor. FIG. 15B
is a sectional view taken along a-a in FIG. 15A when viewed from the -y
side. FIG. 16A is a plan view of a second focus detecting pixel 230SB as
one pixel of the image sensor shown in FIG. 2 when viewed from the
light-receiving surface side (+z side) of the image sensor. FIG. 16B is a
sectional view taken along b-b in FIG. 16A when viewed from the -y side.
FIG. 17A is a plan view of a first image forming pixel 230G as one pixel
of the image sensor shown in FIG. 2 when viewed from the light-receiving
surface side (+z side) of the image sensor. FIG. 17B is a sectional view
taken along c-c in FIG. 17A when viewed from the -y side.

[0096] As shown in FIG. 15B, the first focus detecting pixel 230SA has an
intralayer lens 306 between a microlens 305 and a first light-shielding
layer 330a having the first opening. As shown in FIG. 16B, the second
focus detecting pixel 230SB has an intralayer lens 306 between a
microlens 305 and a second light-shielding layer 330b having the second
opening. As shown in FIG. 17B, no intralayer lens 306 is formed on the
image forming pixel 230G. Other components are the same as those in
arrangement 1 in the first embodiment.

[0097] [Arrangement 2]

[0098] As in arrangement 1, an intralayer lens 306 is formed on each of a
first focus detecting pixel 220SA and second focus detecting pixel 220SB
of a focus detecting pixel group 220 in arrangement 2. The same applies
to a first focus detecting pixel 240SA and second focus detecting pixel
240SB of a focus detecting pixel group 240. Other components are the same
as those in arrangement 2 in the first embodiment.

[0099] [Arrangement 3]

[0100] A focus detecting pixel group 210 in arrangement 3 will be
described below. FIG. 18A is a plan view of a first focus detecting
element 210SA as one pixel of the image sensor shown in FIG. 2 when
viewed from the light-receiving surface side (+z side) of the image
sensor. FIG. 18B is a sectional view taken along a-a in FIG. 18A when
viewed from the -y side. FIG. 19A is a plan view of a second focus
detecting element 210SB as one pixel of the image sensor shown in FIG. 2
when viewed from the light-receiving surface side (+z side) of the image
sensor. FIG. 19B is a sectional view taken along b-b in FIG. 19A when
viewed from the -y side.

[0101] As shown in FIG. 18B, in a first focus detecting element 210SA, an
intralayer lens 306 is formed between a microlens 305 and a first
light-shielding layer 310a having the first opening so as to be eccentric
in the +x direction. The complex microlens constituted by a microlens and
an intralayer lens is configured to be eccentric in the +x direction.
Likewise, in the second focus detecting element 210SB, an intralayer lens
306 is formed between a microlens 305 and a second light-shielding layer
310b having the second opening so as to be eccentric in the +x direction.
The complex microlens constituted by a microlens and an intralens is
configured to be eccentric in the +x direction. Other components are the
same as those in arrangement 3 in the first embodiment.

[0102] In arrangement 3, the geometric centre of the first opening of the
first light-shielding layer 310a of the first focus detecting element
210SA differs from the geometric centre of the second opening of the
second light-shielding layer 310b of the second focus detecting element
210SB. The average position of the geometric centre of the first opening
of the first light-shielding layer 310a and the geometric centre of the
second opening of the second light-shielding layer 310b is eccentric with
respect to the geometric centre of the light-receiving surface of the
photo-electric conversion portion in the -x direction. The complex
microlenses of the first focus detecting element 210SA and second focus
detecting element 210SB are eccentric with respect to the geometric
centre of the photo-electric conversion portion in the +x direction.

[0103] In contrast to this, a first focus detecting element 250SA and
second focus detecting element 250SB of a focus detecting element group
250 shown in FIG. 2 are configured such that the average position of the
geometric centre of the first opening of the first light-shielding layer
and the geometric centre of the second opening of the second
light-shielding layer is eccentric with respect to the geometric centre
of the light-receiving surface of the photo-electric conversion portion
in the +x direction. The complex microlenses of the first focus detecting
element 250SA and second focus detecting element 250SB are eccentric with
respect to the geometric centre of the light-receiving surface of the
photo-electric conversion portion in the -x direction.

[0104] In this embodiment, the respective complex microlenses of the first
focus detecting pixel and second focus detecting pixel are eccentric in a
direction opposite to the direction in which the average position of the
geometric centre of the first opening and the geometric centre of the
second opening is eccentric. Each of the complex microlenses of the first
focus detecting pixel and second focus detecting pixel is constituted by
a plurality of microlenses.

[0105] Other components are the same as those in the first embodiment.
With the above arrangement, it is possible to enlarge the image height
range in which focus detection can be performed by the pupil division
phase-difference method in accordance with a pupil shift at the
peripheral height of the image sensor.

[0106] While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0107] This application claims the benefit of Japanese Patent Application
No. 2012-232334, filed Oct. 19, 2012, which is hereby incorporated by
reference herein in its entirety.

Patent applications by Koichi Fukuda, Tokyo JP

Patent applications by CANON KABUSHIKI KAISHA

Patent applications in class With optics peculiar to solid-state sensor

Patent applications in all subclasses With optics peculiar to solid-state sensor